Method and apparatus of correcting geometry of an image

ABSTRACT

The present invention relates to a method and apparatus that obtain error correction data by adjusting the LOS vector of a sensor, and assign precise ground coordinates to respective image coordinates of an image using the error correction data and auxiliary data for the image. 
     In the method of correcting geometry of an image using a LOS vector adjustment model of the present invention, an image, obtained by photographing a ground surface, and auxiliary data for the image, are acquired. Ground coordinates for a ground control point, and image coordinates of the image matching the ground coordinates are acquired. A LOS vector of a sensor of a photographing device is adjusted, thus obtaining error correction data. The auxiliary data and the error correction data are applied to LOS vector adjustment models, and ground coordinates are assigned to respective image coordinates of the image, thus performing exterior orientation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication No. PCT/KR2006/003301, filed on Aug. 23, 2006, which claimspriority to Korean Patent Application No. 10-2006-0026655, filed on Mar.23, 2006. These applications are hereby incorporated herein by referencein their entireties.

TECHNICAL FIELD

The present invention relates, in general, to a method and apparatus forcorrecting distortion of an image, taken to investigate thecharacteristics of a ground surface and, more particularly, to a methodand apparatus that can obtain error correction data by adjusting the LOSvector of a sensor, and can assign precise ground coordinates torespective image coordinates of an image using the error correction dataand auxiliary data for the image.

BACKGROUND ART

Currently, an image obtained by photographing a ground surface is mainlycaptured using both a camera and a sensor installed in an airplane or asatellite located at a certain altitude above the ground surface. Anairplane has a relatively low altitude of several hundreds of meters toseveral kilometers, but has relatively unstable velocity and attitude,compared to a satellite. In contrast, a satellite is a photographingdevice, moving outside the atmosphere, and has a very high altitude ofseveral hundreds of kilometers, but has relatively stable velocity andattitude, and moves along a defined elliptical orbit. Further, an aerialphotograph obtained by an airplane is an image having a very highresolution, and is mainly used to produce a topographic map, an imagemap, digital terrain data, etc., having a small or intermediate scale.Satellites have recently become able to take high resolution images, butsuch images are mainly used to manufacture objects related to maps, suchas a topographic map, an image map, digital terrain data, etc., havingan intermediate or large scale due to their relatively low resolution.Satellites include Satellites Pour l' Observation de la Terre (SPOT),Indian Remote Sensing Satellite (IRS), Advanced Land Observing Satellite(ALOS), Land Remote-sensing Satellite (LANDSAT), and commercial earthobservation satellites (IKONOS and QUICKBIRD), and have been used invarious application fields, such as detection in variation related tothe observation of a ground surface, or forest fire monitoring.

The image of the ground surface, taken using a photographing device,such as an airplane or a satellite, is not immediately utilized formilitary or industrial purposes. The reason for this is that the imageof the ground surface is distorted due to the characteristics of thephotographing method.

Therefore, such distortion is corrected, and a precise orthoimage,digital topographic map, three-dimensional image, etc. are produced onthe basis of a corrected image and are utilized for military orindustrial purposes.

In this case, the correction of distortion of an image means anoperation for assigning precise and actual ground coordinates on theground to respective coordinates on the image.

A typical method of correcting the distortion of an image (geometriccorrection) involves the use of a sensor model. As shown in FIG. 1, thesensor model is a formula derived from the relationship between theposition of a photographing device {right arrow over (S)} and theposition of a ground control point {right arrow over (P)} on the basisof the center of the earth, and is a function of image coordinates (i,j) and ground coordinates (P_(x), P_(y), P_(z)). In order to assignground coordinates using a sensor model, auxiliary data, such as theposition, velocity, attitude, and photographing angle of a photographingdevice, in addition to the image coordinates, is required. Suchauxiliary data is provided by the photographing device, together withthe image.

However, there is a problem in that such auxiliary data is not accurate.As shown in FIG. 2, there are errors between the photographing position(S_(c)) and the photographing angle of the actual photographing device,and the photographing position (S) and the photographing angle ({rightarrow over (u)}) according to the auxiliary data. Further, although notshown in the drawing, there is an error between the actual attitude ofthe photographing device and the attitude according to auxiliary data.

As shown in FIG. 2, due to such errors, the position on the groundsurface P_(c) actually taken by the photographing device and theposition on the ground surface P obtained by the sensor model differfrom each other.

Therefore, a method of revising a sensor model has been proposed tominimize errors in the ground coordinates on the ground surface causedby inaccurate auxiliary data.

Conventional methods of revising a sensor model, proposed in the priorart, performs revision so that either or both of the position and theattitude of a photographing device, according to auxiliary data,approach those of the actual photographing device.

A representative conventional method is disclosed in Korean PatentAppln. No. 10-2005-51358 entitled “method of Correcting Geometry of aLinearly Scanned Image Using Photographing Device Rotation Model”.However, currently, the relatively accurate photographing position,photographing velocity and photographing attitude of a photographingdevice can be detected using systems such as a Global Positioning System(GPS) or Doppler Orbitography and Radiopositioning Integrated bySatellite (DORIS). That is, because of such accurate information, if asensor model is revised by adjusting the position or attitude of aphotographing device, errors in ground coordinates may be increasedinstead. Therefore, it is required to more easily and precisely correctthe geometric distortion of an image, obtained by photographing theground surface, by maximally utilizing such accurate information.

DISCLOSURE OF INVENTION Technical Problem

Accordingly, the present invention has been made keeping in mind theabove problems, and an object of the present invention is to provide amethod and apparatus that enable more precise geometric correction usinga LOS vector adjustment model, which has been established by adjustingthe photographing angles (LOS vector) of the sensor of a photographingdevice, and that can reduce the time and cost required for geometriccorrection.

Technical Solution

In order to accomplish the above object, the present invention providesa method of correcting geometry of an image through adjustment of aLine-Of-Sight (LOS) vector, comprising the steps of (a) acquiring animage, obtained by photographing a ground surface, and auxiliary datafor the image; (b) acquiring ground coordinates for a ground controlpoint, and image coordinates of the image matching the groundcoordinates; (c) adjusting a LOS vector of a sensor of a photographingdevice for photographing the image using the auxiliary data acquired atstep (a), and the ground coordinates and the image coordinates acquiredat step (b), thus obtaining error correction data; and (d) applying theauxiliary data acquired at step (a) and the error correction dataobtained at step (c) to LOS vector adjustment models, and assigningground coordinates to respective image coordinates of the image, thusperforming exterior orientation for correcting distortion of the image.

Further, the present invention provides an apparatus for correctinggeometry of an image through adjustment of a LOS vector, comprising animage information extraction unit for extracting information about aposition, velocity or attitude of a photographing device, and a LOSvector of a sensor, from auxiliary data for an image obtained byphotographing a ground surface; a ground control point extraction unitfor receiving and storing ground coordinates for a ground control pointand image coordinates matching the ground coordinates; an errorcorrection data extraction unit for receiving data from the imageinformation extraction unit and the ground control point extractionunit, and then generating error correction data through adjustment ofthe LOS vector of the sensor; and an exterior orientation calculationunit for receiving data from the image information extraction unit andthe error correction data extraction unit and applying the data to LOSvector adjustment models, thus calculating ground coordinatescorresponding to respective image coordinates of the image.

Advantageous Effects

As described above, the present invention can simplify a calculationprocedure for extracting ground coordinates, thus reducing the cost andtime required for geometric correction, and remarkably increasing theprecision of extracted ground coordinates. Accordingly, the presentinvention is advantageous in that a working process related to theproduction of an orthoimage, an image map, a digital topographic map, ordigital terrain data can be simplified, thus working time can bereduced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a geometric example of a photographing deviceand the geometry of a ground surface;

FIG. 2 is a view showing a geometric example of the adjustment of a LOSvector;

FIG. 3 is a flowchart of a geometric correction method according to thepresent invention; and

FIG. 4 is a schematic block diagram of a geometric correction apparatusaccording to the present invention.

DESCRIPTION OF REFERENCE CHARACTERS OF IMPORTANT PARTS

10: image information extraction unit

20: ground control point extraction unit

30: error correction data extraction unit

40: sensor model calculation unit

50: exterior orientation calculation unit

BEST MODE

As shown in FIG. 2, the present invention adjusts the photographingangles of a sensor (Line-Of-Sight [LOS] vector) among auxiliary data foran image, thus minimizing an error between a position on a groundsurface P_(c), taken by an actual photographing device, and a positionon the ground surface, obtained when auxiliary data, including theadjusted photographing angle {right arrow over (u)}, is applied to LOSvector adjustment models.

First, LOS vector adjustment models, established in the presentinvention, are described.

As shown in FIG. 1, the device for photographing the ground surface hasa LOS vector {right arrow over (u)} directed from the position of thephotographing device S, and photographs a position P on the groundsurface. If the position of the photographing device from the center ofthe earth is represented by a vector {right arrow over (S)}, and theposition on the ground surface from the center of the earth isrepresented by a vector {right arrow over (P)},

the following Equation is obtained.{right arrow over (P)}−{right arrow over (S)}=μ·{right arrow over(u)}  [Equation 1]

In this case, μ is a parameter. However, the values of the vectors{right arrow over (P)} and {right arrow over (S)}, well known in theart, are represented by an Earth-Centered Earth-Fixed Coordinate System(ECEF) or an Earth-Centered Inertia Coordinate System (ECI), and thevalue of the vector {right arrow over (u)} is represented by an AttitudeCoordinate System (ACS). Since the three vectors are based on differentcoordinate systems, the different coordinate systems must be adjusted tothe same coordinate system. In order to adjust the different coordinatesystems to a local orbital coordinate system, an attitude coordinaterotation matrix for converting the attitude coordinate system into thelocal orbital coordinate system, and a position coordinate rotationmatrix for converting the local orbital coordinate system into theearth-centered earth-fixed coordinate system, are used. The attitudecoordinate rotation matrix and the position coordinate rotation matrixare given in the following Equations 2 and 3. If the above Equation 1 isrepresented again using Equations 2 and 3, the following Equation 4 isobtained.

$\begin{matrix}{M = \begin{bmatrix}\frac{\overset{\rightarrow}{S} \times \left( {\overset{\rightarrow}{V} \times \overset{\rightarrow}{S}} \right)}{{\overset{\rightarrow}{S} \times \left( {\overset{\rightarrow}{V} \times \overset{\rightarrow}{S}} \right)}} \\\frac{\overset{\rightarrow}{V} \times \overset{\rightarrow}{S}}{{\overset{\rightarrow}{V} \times \overset{\rightarrow}{S}}} \\\frac{\overset{\rightarrow}{S}}{\overset{\rightarrow}{S}}\end{bmatrix}} & \left\lbrack {{{Equation}\mspace{14mu} 2\text{-}1},{{for}\mspace{14mu}{airplane}}} \right\rbrack \\{M = {\begin{bmatrix}{\cos\;\Omega} & {{- \sin}\;\Omega} & 0 \\{\sin\;\Omega} & {\cos\;\Omega} & 0 \\0 & 0 & 1\end{bmatrix} \cdot {\quad{\begin{bmatrix}1 & 0 & 0 \\0 & {\cos\; I} & {{- \sin}\; I} \\0 & {\sin\; I} & {\cos\; I}\end{bmatrix} \cdot \begin{bmatrix}{{- \sin}\; W} & 0 & {\cos\; W} \\{\cos\; W} & 0 & {\sin\; W} \\0 & 0 & 1\end{bmatrix}}}}} & \left\lbrack {{{Equation}\mspace{14mu} 2\text{-}2},{{for}\mspace{14mu}{satellite}}} \right\rbrack \\{A = {\begin{bmatrix}{\cos\;\kappa} & {{- \sin}\;\kappa} & 0 \\{\sin\;\kappa} & {\cos\;\kappa} & 0 \\0 & 0 & 1\end{bmatrix} \cdot {\quad{\begin{bmatrix}{\cos\;\varphi} & 0 & {\sin\;\varphi} \\0 & 1 & 0 \\{{- \sin}\;\varphi} & 0 & {\cos\;\varphi}\end{bmatrix} \cdot {\quad\begin{bmatrix}1 & 0 & 0 \\0 & {\cos\;\omega} & {\sin\;\omega} \\0 & {\sin\;\omega} & {\cos\;\omega}\end{bmatrix}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In this case, ω is a roll angle, φ is a pitch angle, χ is a yaw angle,{right arrow over (S)} is the position vector of the photographingdevice, {right arrow over (V)} is the velocity vector of thephotographing device, is the longitude of an ascending node, is theinclination of an orbit, and is the argument of latitude of a satellite,which is the Kepler element.

$\begin{matrix}{{{M^{- 1} \cdot \begin{bmatrix}P_{x} \\P_{y} \\P_{z}\end{bmatrix}} - \begin{bmatrix}0 \\0 \\\rho\end{bmatrix}} = {µ\;{A \cdot \begin{bmatrix}u_{x} \\u_{y} \\u_{z}\end{bmatrix}}}} & \left\lbrack {{Equation}\mspace{20mu} 4} \right\rbrack\end{matrix}$

In this case P_(x), P_(y), P_(z) and u_(x), u_(y), u_(z) are elements of{right arrow over (P)} and {right arrow over (u)}, respectively, and Pis the distance from the center of the earth to the photographingdevice, and is identical to |{right arrow over (S)}|. Further, x, y andz are directional components, with z indicating the direction from thecenter of the earth to the photographing device, x indicating themovement direction of the photographing device, and y indicating thedirection perpendicular to x and z directions according to the RightHand Rule.

If the coordinate transformation matrix is removed from the right termin Equation 4, and properties indicating that M⁻¹=M^(T) and A⁻¹=A^(T)are used, Equation 4 can be represented again by the following Equation.

$\begin{matrix}{{{\left( {M \cdot A} \right)^{T} \cdot \begin{bmatrix}P_{x} \\P_{y} \\P_{z}\end{bmatrix}} - {A^{T} \cdot \begin{bmatrix}0 \\0 \\\rho\end{bmatrix}}} = {µ\begin{bmatrix}u_{x} \\u_{y} \\u_{z}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{20mu} 5} \right\rbrack\end{matrix}$

If Equation 5 is simplified, the following Equation is obtained.

$\begin{matrix}{{{\begin{bmatrix}r_{11} & r_{12} & r_{13} \\r_{21} & r_{22} & r_{23} \\r_{31} & r_{32} & r_{33}\end{bmatrix}\begin{bmatrix}P_{x} \\P_{y} \\P_{z}\end{bmatrix}} - {\begin{bmatrix}a_{11} & a_{12} & a_{13} \\a_{21} & a_{22} & a_{23} \\a_{31} & a_{32} & a_{33}\end{bmatrix}\begin{bmatrix}0 \\0 \\\rho\end{bmatrix}}} = {µ\begin{bmatrix}{\tan\left( \Psi_{x} \right)} \\{\tan\left( \Psi_{y} \right)} \\{- 1}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{20mu} 6} \right\rbrack\end{matrix}$

In this case, α is the element of the rotation matrix A, r is theelement of a matrix R=(M·A)^(T), and ψ_(x) and ψ_(y) are photographingangles in x and y directions.

If the parameter μ is eliminated from Equation 6, two equations, whichare sensor models defined by the photographing angles, are realized, asshown in the following Equations.

$\begin{matrix}{F_{1} = {{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 7} \right\rbrack \\{{F_{2} = {{{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x}} = 0}}{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack}\mspace{14mu}{and}}{{{In}\mspace{14mu}{this}\mspace{14mu}{case}},{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack}}} & \left\lbrack {{Equation}\mspace{20mu} 8} \right\rbrack\end{matrix}$

are the photographing angles of the sensor, obtained using the position,velocity and attitude of the photographing device among the auxiliarydata.

The sensor models of the present invention represented by Equations 7and 8 are sensor models having a new format, differing from conventionalsensor models (collinearity equations, sensor models disclosed in KoreanPatent Appln. No. 10-2005-51358, etc.).

For reference, α and r in the sensor models are functions of the time tfor which an image is taken, the photographing time t is proportional tothe number of lines i, and ψ_(x) and ψ_(y) are functions of the numberof columns j. Therefore, the sensor models represent the relationshipbetween the image coordinates (i, j) and the ground coordinates (P_(x),P_(y), P_(z)).

If precise ground coordinates and precise image coordinates at any onepoint are applied to Equations 7 and 8 when there is no distortion in animage, F₁=F₂=0 will be satisfied. However, due to distortion, F₁ and F₂have a value other than 0, which indicates the amount of distortion ofthe image. The units in Equations 7 and 8 are angles (degrees).Therefore, the amount of distortion is also represented by degrees, butit is difficult to determine the amount of distortion using degrees.Therefore, it is preferable that a scale factor k be multiplied by theresults of Equations 7 and 8 (k^(F1) and k^(F2)) to convert such degreesinto distances. The scale factor is defined by k=h/cos(ψ_(c)) using theheight of a satellite h, and the photographing angle ψ_(c) at the centerof the image.

As described above, since the auxiliary data for the image is notaccurate, considerable errors may occur if the ground coordinates(P_(x), P_(y), P_(z)) are assigned to respective image coordinates (i,j) using the sensor models. Therefore, an element required to offsetsuch errors must be added to the sensor models.

The LOS vector adjustment models, in which the element required tooffset the errors is additionally provided, are given by the followingtwo equations.

$\begin{matrix}{F_{1} = {{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x} + E_{x}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 9} \right\rbrack \\{F_{2} = {{{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{y} + E_{y}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 10} \right\rbrack\end{matrix}$

In this case, E_(x) and E_(y) are error correction data, and are valuesrequired to offset errors, which are included in the photographingangles of the sensor of the photographing device that are auxiliary dataand which exist in x and y directions.

The error correction data can be determined by the number of lines i ofthe image and the number of columns j, and can be represented by thefollowing Equations.

$\begin{matrix}{E_{x} = {a_{x\; 0} + {\sum\limits_{m = 0}^{n}\left( {{b_{xm} \cdot i^{m + 1}} + {c_{xm} \cdot j^{m + 1}}} \right)}}} & \left\lbrack {{Equation}\mspace{20mu} 11} \right\rbrack \\{E_{y} = {a_{y\; 0} + {\sum\limits_{m = 0}^{n}\left( {{b_{ym} \cdot i^{m + 1}} + {c_{ym} \cdot j^{m + 1}}} \right)}}} & \left\lbrack {{Equation}\mspace{20mu} 12} \right\rbrack\end{matrix}$

In this case a_(x0), b_(xm), c_(xm), a_(y0), b_(ym) and c_(ym) are thecoefficients of the LOS vector corrected by the ground control point.

Hereinafter, a method of correcting the geometry of an image through theadjustment of a LOS vector according to the present invention isdescribed with reference to the flowchart of FIG. 3.

First, at step (a), an image, obtained by photographing a groundsurface, and auxiliary data for the image are acquired.

The image and the auxiliary data are obtained by a photographing device,such as an airplane or a satellite. In this case, the auxiliary dataincludes position information about a photographing device forphotographing the image, velocity information about the photographingdevice, the time required to photograph the central line of the image,the photographing time per line of the image, attitude information aboutthe photographing device (yaw, pitch and roll), and information aboutthe photographing angles in X and Y directions and the distortion of alens.

After step (a) has been performed, at step (b), a ground control pointis selected, and ground coordinates (P_(x), P_(y), P_(z)) at the groundcontrol point, and the image coordinates (i, j) of the image, matchingthe ground coordinates, are acquired.

The selection of the ground control point is preferably performed toselect a bridge, a building, etc., so that the ground control point canbe easily identified in the image. The ground coordinates for the groundcontrol point are acquired by Global Positioning System (GPS)measurement in a field, or are obtained using digital terrain data. Theimage coordinates matching the ground coordinates are directly acquiredby an operator viewing the image.

In this case, it is preferable that that the sensor models of Equations7 and 8 be used for acquiring the image coordinates matching the groundcoordinates. Since the image includes a considerably wide region, it isnot easy for an operator to detect image coordinates corresponding tothe ground control point in the image without any information.Therefore, if the ground coordinates for the ground control point areapplied to the sensor models to obtain image coordinates through thesensor models, and the surroundings of the image coordinates, obtainedthrough the sensor models, in the image are searched, the imagecoordinates matching the ground coordinates can be easily obtained.

After step (b) has been performed, at step (c), the LOS vector of thesensor of the photographing device for photographing the image isadjusted using the auxiliary data, the ground coordinates and the imagecoordinates, thus acquiring error correction data E_(x) and E_(y).

This operation is described in detail. If the ground coordinates for theground control point, the image coordinates, and the auxiliary data forthe image are applied to Equations 9 and 10, E_(x) and E_(y) are unknownquantities. Since the unknown quantities E_(x) and E_(y) are functionsof the image coordinates (i, j), as indicated in Equations 11 and 12,a_(x0), b_(xm), c_(xm), a_(y0), b_(ym) and c_(ym), which are thecoefficients of the LOS vector, are unknown quantities. Consequently, ifthe coefficients of the LOS vector are determined, error correction datais obtained.

If the number of ground control points is one, E_(x) and E_(y) arecalculated up to 0-th order terms of i and j (that is, a_(x0) anda_(y0)). If the number of ground control points is two, E_(x) and E_(y)are calculated up to first order terms of i and j (that is, a_(x0),b_(xm), c_(xm), ay_(y0), b_(ym) and c_(ym)). If the number of groundcontrol points is n, E_(x) and E_(y) are calculated up to n-i-th orderterms of i and j. Accordingly, E_(x) and E_(y) are obtained.

In this case, E_(x) and E_(y) are preferably calculated up to the firstorder terms of i and j (that is, when the number of ground controlpoints is two). As a result of experiments, if calculation is performedup to 0-th order terms, a lot of errors occur, whereas, if calculationis performed up to second or higher order terms, the calculationprocedure is complicated, and over-correction errors occur.

As described above, error correction data E_(x) and E_(y) are obtainedusing Equations 9, 10, 11 and 12, and the coefficients thereof areobtained using normal equations generally used in engineering fields. Acalculation procedure using normal equations is well known in the art,so a detailed description thereof is omitted.

After step (c) has been performed, at step (d), exterior orientation forcorrecting the distortion of the image is performed by applying theauxiliary data for the image and the error correction data to LOS vectoradjustment models, and by assigning ground coordinates to respectiveimage coordinates of the image.

The auxiliary data, the error correction data and the image coordinatesare applied to Equations 9 and 10, and thus the ground coordinates(P_(x), P_(y), P_(z)) are obtained. The number of equations is two, andthe number of unknown quantities is three. Therefore, it is impossibleto calculate ground coordinates using only a single image, obtained byphotographing the ground surface, and thus another image, obtained byphotographing the same ground surface, is additionally required. Then,since two equations are obtained from the first image, and two equationsare obtained from the second image, the ground coordinates can becalculated.

After step (d) has been performed in this way, the image is providedwith information about the ground coordinates. Therefore, it is possibleto produce a three-dimensional image on the basis of the information, toproduce an orthoimage through the rearrangement of the locations ofpixels, and to produce a digital topographic map, digital terrain data,etc.

Further, for reference, if the attitude of the photographing device isadjusted, results similar to those obtained when the photographing angleof the sensor is adjusted can be obtained from an external point ofview. However, when the attitude of the photographing device isadjusted, the calculation procedure thereof is considerably complicated,thus increasing the time required to extract ground coordinates.Further, it is difficult to effectively correct errors, occurring in thedirection of pixels (j or x direction), through the use of a function oftime t, that is, a function of the direction of lines (i or ydirection).

Hereinafter, an apparatus for correcting the geometry of an imagethrough the adjustment of a LOS vector according to the presentinvention is described with reference to FIG. 4, which shows a blockdiagram.

It is impossible in practice to perform the correction of geometry of animage through a manual operation. Therefore, geometry is corrected usinga device such as a computer. The geometric correction apparatusaccording to the present invention is required for such an operation.

As shown in FIG. 4, the geometric correction apparatus according to thepresent invention includes an image information extraction unit 10, aground control point extraction unit 20, an error correction dataextraction unit 30, an exterior orientation calculation unit 50, and asensor model calculation unit 40.

The image information extraction unit 10 extracts the position, velocityand attitude of a photographing device, and a LOS vector of the sensorof the photographing device, which are information required to correctgeometric distortion, from auxiliary data for an input image.

The ground control point extraction unit 20 receives and stores groundcoordinates and image coordinates for a plurality of ground controlpoints. The ground coordinates and the image coordinates are input by anoperator.

The sensor model calculation unit 40 is required to allow the operatorto easily detect image coordinates which match ground coordinates. Theimage coordinates are detected by the operator viewing the image. It isnot easy to detect any one point corresponding to a ground control pointin the image obtained by photographing a wide region. Therefore, thesensor model calculation unit 40 receives data from the imageinformation extraction unit and ground coordinates from the groundcontrol point extraction unit, and calculates the data and the groundcoordinates, thus obtaining image coordinates. The image coordinatesbased on sensor models may contain errors, but approach precise imagecoordinates. Therefore, the operator searches the surroundings of theimage coordinates of the image, calculated based on the sensor models,thus easily detecting precise image coordinates.

The error information extraction unit 30 receives data from the imageinformation extraction unit 10 and the ground control point extractionunit 20, and then generates error correction data E_(x) and E_(y)through the adjustment of the LOS vector of the sensor of thephotographing device.

The exterior orientation calculation unit 50 receives data from theimage information extraction unit 10 and the error correction dataextraction unit 30, applies the received data to the above Equations 9and 10, which are LOS vector adjustment models, and then calculatesground coordinates corresponding to respective image coordinates of theimage.

Although the method and apparatus for correcting the geometry of animage through LOS vector adjustment, having specific steps andcomponents, have been described with reference to the attached drawingsin the course of description of the present invention, those skilled inthe art will appreciate that various modifications, additions andsubstitutions are possible. The modifications, additions andsubstitutions should be interpreted as being included in the scope ofthe present invention.

1. A method for correcting geometry of an image using a Line-Of-Sight(LOS) vector adjustment model, the method comprising: acquiring an imageand auxiliary data for the image, the image obtained by photographing aground surface; acquiring ground coordinates for a ground control pointand image coordinates of the image matching the ground coordinates;adjusting a LOS vector of a sensor of a photographing device used tophotograph for photographing the image using the auxiliary dataacquired; and adjusting the ground coordinates and the image coordinatesacquired, thus obtaining error correction data; and applying theacquired auxiliary data and the obtained error correction data obtainedto LOS vector adjustment models, and assigning ground coordinates tocorresponding image coordinates of the image, thus performing exteriororientation for correcting distortion of the image, wherein acquiringimage coordinates matching the ground coordinates is performed usingimage coordinates based on sensor models that are obtained using sensormodels represented by the following Equations 7 and 8: $\begin{matrix}{F_{1} = {{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x}} = 0}} & \left\lbrack {{Equation}\mspace{14mu} 7} \right\rbrack \\{F_{2} = {{{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{y}} = 0}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$ where (P_(x), P_(y), P_(z)) are ground coordinates for theground control point, ρ is the distance from the center of the earth tothe photographing device, and${\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack}\mspace{14mu}{and}\mspace{14mu}{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack}\mspace{14mu}{are}$photographing angles of the sensor among the auxiliary data, and ψ_(x)and ψ_(y) are photographing angles of the sensor, obtained using aposition, velocity and attitude of the photographing device, among theauxiliary data, F₁ and F₂ are residual errors due to distortion ofimage, r₁₁ to r₃₃ are the elements of R=(M·A)^(T), the positioncoordinate rotation matrix (M) and the attitude coordination rotationmatrix (A) follow ${{M^{- 1} \cdot \begin{bmatrix}P_{x} \\P_{y} \\P_{z}\end{bmatrix} \cdot \begin{bmatrix}0 \\0 \\\rho\end{bmatrix}} = {µ\;{A \cdot \begin{bmatrix}u_{x} \\u_{y} \\u_{z}\end{bmatrix}}}},u_{x},u_{y},u_{z}$  are the elements of the LOS vector({right arrow over (u)}) and μ is the parameter related with {rightarrow over (u)} and {right arrow over (P)} and E_(x) and E_(y) are errorcorrection data in x and y directions.
 2. The method according to claim1, wherein the LOS vector adjustment models are represented by thefollowing Equations 9 and 10: $\begin{matrix}{F_{1} = {{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x} + E_{x}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 9} \right\rbrack \\{F_{2} = {{{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{y} + E_{y}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 10} \right\rbrack\end{matrix}$ where E_(x) and E_(y) are error correction data in x and ydirections.
 3. The method according to claim 2, wherein the errorcorrection data is obtained using the following Equations 11 and 12:$\begin{matrix}{E_{x} = {a_{x\; 0} + {\sum\limits_{m = 0}^{n}\left( {{b_{xm} \cdot i^{m + 1}} + {c_{xm} \cdot j^{m + 1}}} \right)}}} & \left\lbrack {{Equation}\mspace{20mu} 11} \right\rbrack \\{E_{y} = {a_{y\; 0} + {\sum\limits_{m = 0}^{n}\left( {{b_{ym} \cdot i^{m + 1}} + {c_{ym} \cdot j^{m + 1}}} \right)}}} & \left\lbrack {{Equation}\mspace{20mu} 12} \right\rbrack\end{matrix}$ where a_(x0), b_(xm), c_(xm), a_(y0), b_(ym) and c_(ym)are coefficients of the LOS vector corrected by the ground controlpoint, i is a line of the image, and j is a column of the image.
 4. Themethod according to claim 3, wherein the error correction data is avalue calculated up to first order terms of i and j.
 5. An apparatus forcorrecting geometry of an image using a LOS vector adjustment model, theapparatus comprising: an image information extraction unit configured toacquire an image and auxiliary data for the image, the image beingobtained by photographing a ground surface; a ground control pointextraction unit configured to receive and store ground coordinates for aground control point and image coordinates matching the groundcoordinates; an error correction data extraction unit configured toreceive the auxiliary data from the image information extraction unitand the ground coordinates and the image coordinates from the groundcontrol point extraction unit, and then generate error correction datathrough adjustment of a LOS vector of the sensor of a photographingdevice for photographing the image; and an exterior orientationcalculation unit configured to receive the auxiliary data from the imageinformation extraction unit and the error correction data from the errorcorrection data extraction unit and apply the data to LOS vectoradjustment models, thus calculating ground coordinates corresponding torespective image coordinates of the image, wherein the LOS vectoradjustment models used for the exterior orientation calculation unit arerepresented by the following Equations 9 and 10: $\begin{matrix}{F_{1} = {{{\tan^{- 1}\left\lbrack \frac{{r_{11}p_{x}} + {r_{12}p_{y}} + {r_{13}p_{z}} - {a_{31}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{x} + E_{x}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 9} \right\rbrack \\{F_{2} = {{{\tan^{- 1}\left\lbrack \frac{{r_{21}p_{x}} + {r_{22}p_{y}} + {r_{23}p_{z}} - {a_{32}\rho}}{{r_{31}p_{x}} + {r_{32}p_{y}} + {r_{33}p_{z}} - {a_{33}\rho}} \right\rbrack} + \Psi_{y} + E_{y}} = 0}} & \left\lbrack {{Equation}\mspace{20mu} 10} \right\rbrack\end{matrix}$ where (P_(x), P_(y), P_(z)) are ground coordinates for theground control point, ρ is the distance from the center of the earth tothe photographing device, and are photographing angles of the sensoramong the auxiliary data, and Ψ_(x) and Ψ_(y) are photographing anglesof the sensor, obtained using a position, velocity and attitude of thephotographing device, among the auxiliary data, F₁ and F₂ are residualerrors due to distortion of image, r₁₁ to r₃₃ are the elements ofR=(M·A)^(T), the position coordinate rotation matrix (M) and theattitude coordination rotation matrix (A) follow${{M^{- 1} \cdot \begin{bmatrix}P_{x} \\P_{y} \\P_{z}\end{bmatrix} \cdot \begin{bmatrix}0 \\0 \\\rho\end{bmatrix}} = {µ\;{A \cdot \begin{bmatrix}u_{x} \\u_{y} \\u_{z}\end{bmatrix}}}},u_{x},u_{y},u_{z}$  are the elements of the LOS vector({right arrow over (u)}) and μ is the parameter related with {rightarrow over (u)} and {right arrow over (P)}, and E_(x) and E_(y) areerror correction data in x and y directions.
 6. The apparatus accordingto claim 5, further comprising a sensor model calculation unitconfigured to detect image coordinates matching the ground coordinates,and receive data from the image information extraction unit and theground coordinates from the ground control point extraction unit, thuscalculating image coordinates based on sensor models.